The invention concerns a measuring cable travel sensor and more particularly a measuring cable travel sensor with housing.
Measuring cable travel sensors are travel or distance-measuring sensors which operate on the principle of a measuring cable, with a housing which is suitable for use in industrial situations. A typical travel sensor of that kind comprises a precisely defined and positioned cable drum on to which a measuring cable is wound, generally only in a single layer on the drum, with one end of the measuring cable being suitably fixed to the cable drum. The other free end of the measuring cable is secured to that body or article, the variation in the position of which is to be precisely measured.
When the movable body or article moves away from or towards the cable drum of the measuring cable travel sensor, the resulting angular movements of the measuring cable drum about its axis are converted into a precise travel or distance length by means of a rotary angle sensor which is non-rotatably coupled to the cable drum. A rotary torsion spring which is operatively connected to the cable drum, generally in coaxial relationship therewith, ensures that the measuring cable is wound on to the cable drum again when the movable body whose position is to be measured moves towards the cable drum, thereby to ensure that the measuring cable is properly wound on to the drum and is kept in a reasonably taut condition.
The housing for a typical measuring cable travel sensor of such a kind which in particular has receiving regions for accommodating the cable drum and the spring is assembled from individual parts, in particular by screw means. The one individual part provides a receiving region for accommodating the spring, a further part provides a receiving region for accommodating the cable drum and there is possibly yet a further part which provides a receiving region for the rotary angle sensor. The individual parts constituting the housing of the measuring cable travel sensor of such a configuration are generally produced more particularly from light metal or alloy by a die casting process and subjected to finishing machining by procedures such as milling and boring, but they may also be produced from the solid by cutting machining. The parts constituting the housing can also be produced by deep drawing.
It has been found however that housings of that nature suffer from a number of specific disadvantages according to the respective mode of manufacture involved.
Thus for example all forms of housing which are produced by means of an initial shaping mold as is the case for example with die casting or deep drawing are an economical proposition only when relatively large numbers of housings are produced.
On the other hand housing parts which are produced for example by milling from solid material are uniformly expensive in regard to individual item price.
An object of the present invention is to provide a measuring cable travel sensor whose parts and in particular the parts of the housing thereof can be easily and inexpensively produced.
Another object of the present invention is to provide a measuring cable travel sensor in which in particular moving parts of the sensor and more especially the cable drum thereof are to be of the lowest viable inertial mass.
Still another object of the present invention is to provide a measuring cable travel sensor having a housing which can be produced in a compact and robust design configuration by a simple operating procedure.
Yet another object of the present invention is to afford a measuring cable travel sensor having a housing whose design configuration is such as to provide a highly advantageous relationship between quality and price by suitable selection of the material involved and the operating procedure applied thereto.
Still a further object of the present invention is to provide a measuring cable travel sensor which is so designed that assembly thereof is a readily implementable procedure.
In accordance with the principles of the present invention the foregoing and other objects are attained by a measuring cable travel sensor comprising a housing accommodating a measuring cable drum and a rotary spring for urging the cable drum in the cable winding-on direction. A rotary angle sensor is mounted to the housing. The housing at least partially comprises a straight profile portion with a cross-section which is uniform in the longitudinal direction.
As will be appreciated from the description hereinafter in greater detail of preferred embodiments of the present invention, the fact that the measuring cable travel sensor is at least partially manufactured from straight profile portions which are not produced in the required length directly from manufacture, it is possible to use inexpensive extruded profile portions which then only have to be cut to the desired length in order to serve as a portion of the housing or as a part of the cable drum.
The profile portion may include integrated longitudinal grooves of an undercut configuration, whereby it is further possible for covers to be fixed on the open sides of the profile portions by means of self-tapping screws, without requiring further preliminary preparation or machining thereof. Thus the only preliminary preparation operation is that of providing openings on the appropriate profile portion for fitting therethrough the shaft of the measuring cable travel sensor, which carries the rotary members thereof.
It is possible in that way to produce a compact robust housing at low cost, while in addition the relationship between price and quality can also be influenced by the choice of the material used, in particular involving a selection between plastic material and light metal or alloy.
It will be noted in that respect that it is possible to use different profile shapes for the housing, for example either open profile shapes such as a plate profile, an L-shaped profile or a C-shaped profile, or closed profile shapes such as a box profile or a double-box profile. When the open profile shapes are adopted, the cable drum is arranged parallel to one of the main limbs or sides of the profile shape, the shaft carrying the cable drum passing through that limb. More particularly in that case the cable drum is disposed in the free space defined within a C-shaped profile or in the free space between the legs of an L-shaped profile. In such a case the cable drum on the one hand and the rotary spring on the other hand, and possibly additionally also the rotary angle sensor on the other hand, may be disposed in respective separate housing portions which can be releasably fixed to each other, more particularly by screw means.
In particular upon assembly of the rotary spring which is generally a shaped flat spring wound in a spiral configuration in one plane, the procedure involved is such that the spring is on the one hand non-rotatably connected to the shaft and on the other hand fixedly connected to the housing, and the part of the housing which accommodates the spring, which can be referred to hereinafter as the spring shell portion of the housing, is then turned relative to the other parts of the housing, about the shaft, until the spring is in its prestressed condition. It is only then that the spring shell portion constituting part of the housing is connected to the other parts of the housing as for example by screw means or in some other suitable fashion.
When box profile portions are used, on the one hand the spring and on the other hand the cable drum can each be disposed in a respective box profile portion, while in some cases the rotary angle sensor can also be disposed in a further box profile portion. In that case the three box profile portions constituting the housing can be connected directly or indirectly by means of longitudinal covers which engage thereover and which are secured for example by screw means to all three profile portions.
When the housing is made up at least in part by the use of a multiple-box profile portion such as for example a double-box profile portion, the spring on the one hand and the cable drum on the other hand are disposed in respective ones of the cavities defined by the box profile, while the rotary angle sensor can possibly be disposed in a third cavity in the profile portion.
In a preferred feature of the invention the axial direction of the shaft which connects the rotary parts of the sensor extends transversely with respect to the longitudinal direction of the profile portion and passes through its main limb which can involve an increased wall thickness or gauge in comparison with secondary limbs, for mounting plain or rolling bearings. In addition in a further preferred feature the profile portions can be provided with integral base plates which project laterally outwardly at least on one side and which serve to connect the measuring cable travel sensor to other components, for example of a structure on which the measuring cable travel sensor is to be mounted.
For the purposes of appropriately distributing the movable masses of the assembly, the spring on the one hand and the rotary angle sensor on the other hand can be disposed on mutually opposite sides of the cable drum. Another option in this respect is for the spring to be disposed between the rotary angle sensor and the cable drum, and this structure is preferred in particular in relation to uses in which the receiving region for accommodating the cable drum does not have to be closed off, by virtue of the measuring cable travel sensor being employed in a clean environment. In that way it is possible for the cable drum to be arranged on the one side of the main limb of an open profile while the spring can be arranged on the other side of the main limb. It will be seen therefore that the main limb of the open profile represents the load-bearing function of the housing.
In this case also, in accordance with a further feature, the rotary angle sensor, irrespective of the end of the shaft at which it is arranged, is to be prevented from being entrained in a rotational movement with the cable drum, by way of a torque-resistant support means.
The above-mentioned grooves of an undercut configuration can serve on the one hand for screwing longitudinal covers in position by means of self-tapping screws, but they can also provide for the insertion of boards with electronic circuits and components in the longitudinal direction, something which is possible in particular when the longitudinal grooves are arranged in mutually opposite paired relationship in the case of a profile portion having two limbs which extend parallel to each other.
Intermediate angle portions for mounting further components, for example a brake for the cable drum and so forth, can also be easily fixed by screw means in the longitudinal grooves.
In that respect, a brake on the cable drum and/or the spring is intended to operate in particular only in the measuring cable winding-on direction, and is appropriate and meaningful for those situations of use in which winding-on of the measuring cable can take place so quickly that it would be possible for the measuring cable not to wind on to the cable drum in the correct layered and dense configuration thereon, by virtue of the winding-on speed being excessively high.
In accordance with a preferred feature of the invention the brake may be a fluid brake, operable for example with air or with a suitable liquid, an eddy current brake or a magnetic brake, but preferably always being a brake which does not suffer from wear, thereby to afford enhanced freedom from maintenance requirements.
In an equally simple and inexpensive manner to the housing being at least partially formed from a straight profile portion, the cable drum itself may also at least partially comprise a profile portion. It is to be noted in that respect that the cable drum is to be of the minimum viable inertial mass.
More particularly the winding surface of the cable drum, on to which the measuring cable is wound and from which it is unwound, may comprise a part of a round tubular profile portion, with a central hub to which that part of the tubular profile portion can be connected for example by way of spokes which thus afford a low mass. In that arrangement, the spokes can be formed together with the winding surface and the hub in an integral structure in the form of a special profile portion, the longitudinal direction of which corresponds to the axis of rotation of the cable drum.
It is however also possible for the connection between the winding surface and the hub of the cable drum to be implemented by way of the check or end guide disks which are necessary in any case and which project radially beyond the winding surface, in which respect the central bore in the disks, possibly supplemented by means of spacer elements between the disks, can be sufficient to act as the hub. In order to ensure good dimensional accuracy of the cable drum and to preclude distortion upon assembly thereof, the individual parts making up the cable drum are preferably assembled by adhesive means or by means of positively locking sheet bending connecting means. depending on whether the cable drum comprises sheet metal or plastic material. Combinations of individual parts of different materials are also possible in that respect.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments thereof.